Models of Material Behaviour

In the first epoch of the Earthquake Engineering, the most used model of material behavior was the linear elastic. Gradually, models of nonlinear behavior started to be used in studies of dynamic response of buildings. The use of non linear models would be the second epoch. This second epoch overlaps with the first.

Nowadays, linear elastic models are rarely used to evaluate the dynamic response of buildings covered by the ASCE 7-05 design code.

The first models of non linear behavior were simple models. One story buildings were idealized with four frames, where each frame is substituted by a SB element. These SB have an elastic perfect-plastic behavior. Many studies were done with this type of models. Dissertation Layout

The main issue with these models is that the philosophy of Capacity Design postulates strong column-weak beam plastic mechanisms as a design goal. Most recent studies idealize framed structures with bar elements, to model columns and beams individually. The non linear behavior is introduced into these elements using the concept of plastic hinge (PH). The PH is a convenient simplification that transforms a complex local phenomenon into a mathematical model easier to handle. The behavior of these PH is modeled with an elastic perfect-plastic relationship (as used in this Dissertation). Other models of material behavior that could be used are the bilinear relationships with strain hardening, trilinear relationships, etc.

In recent studies, more sophisticated models are used. The advances in computer machines and structural analysis software, has given to researchers the possibility of including strength and stiffness degradation models. The inconvenient of these models is that their reliability is limited, specially for reinforced concrete structures. However, it seems reasonable to expect some changes in the observed patterns of behavior, with respect to the ones observed for the less sophisticated models, e.g., the elastic perfect-plastic relationship. Dissertation Layout